North Korea pulled its staff out of a joint liaison office with South Korea on Friday on short notice, the South's Unification Ministry said.
Since the office was set up in an industrial park in Kaesong near the North Korean border with the South in September, weekly meetings had been held between the two sides. But no meeting has been held since Feb. 22.
The North Korean side has explained the staff withdrawal as being at the instruction of superiors, the ministry said, adding that it hopes the staff will return quickly to normalize the office's operations.
in Seoul, the National Security Council held a meeting on the issue, but details of the discussions were not immediately available.
North Korea and the United States held a second summit on Feb. 27 and 28, but the talks ended without a deal. Since then, there has been speculation that Pyongyang may also have become more cautious about its relationship with Seoul.
North Korea has repeatedly expressed frustrations with the lack of progress in joint economic projects with South Korea due to ongoing international sanctions.